The present invention relates to printing and scanning test patterns which are used for various calibration adjustments of multiple-printhead inkjet printing systems.
Inkjet cartridges are now well known in the art and generally comprise a body containing an ink supply and having electrically conductive interconnect pads thereon and a printhead for ejecting ink through numerous nozzles in a printhead. In thermally activated inkjet cartridges, each cartridge has heater circuits and resistors which are energised via electrical signals sent through the interconnect pads on the cartridge. Each inkjet printer can have a plurality, often four, of cartridges each one having a different colour ink supply for example black, magenta, cyan and yellow, removably mounted in a printer carriage which scans backwards and forwards across a print medium, for example paper, in successive swaths. When the printer carriage correctly positions one of the cartridges over a given location on the print medium, a jet of ink is ejected from a nozzle to provide a pixel of ink at a precisely defined location. The mosaic of pixels thus created provides a desired composite image.
When multiple printheads are used, it is desirable to provide calibration techniques for alignment adjustments between different printheads as well as between different nozzle arrays in the same printhead.
The present invention provides a technique for adjustable alignment of multiple inkjet printhead cartridges removably mounted on a scanning printer carriage of an inkjet printer by printing and scanning multiple test patterns. The apparatus comprises means for determining the position of the printer carriage along its scanning direction (such as an encoder strip), an optical sensor mounted on the printer carriage and various calibration test patterns which are optically detectable by the optical sensor. Although an optical sensor mounted on the printer carriage of an inkjet printer is known to be useful for a number of purposes related to the scanning of test patterns printed in the print zone of the printer, the present invention extends the usefulness of such an optical sensor for additional types to calibration patterns.
Preferably, the optical sensor is able to distinguish between the reflectance of sensed objects and multiple reference bars of each different color produce changes of reflectance in the scanning direction of the printer carriage as well as in the media advance axis.
According to a further aspect of the present invention there is provided a method of locating a scanning printer carriage of an inkjet printer relative to a series of horizontally or vertically spaced-apart bars, activating an optical sensor mounted on the printer carriage, moving the printer carriage along in its scanning direction or scanning along the media advance axis while optically sensing the bars forming the test pattern, and storing for future use the position of the printer carriage at which the reference mark has been located.
Preferably the process of calibrating the location of the printer carriage is performed several times and between each printhead periodically as needed, as, for example, whenever a new print cartridge (also called xe2x80x9cpenxe2x80x9d herein) is installed.
A more complete understanding of the present invention and other objects, aspects, aims and advantages thereof will be gained from a consideration of the following description of the preferred embodiment read in conjunction with the accompanying drawings provided herein.